Most vehicles in operation today are powered by internal combustion (IC) engines. Internal combustion engines typically have a plurality of cylinders or other working chambers. An air-fuel mixture is delivered to each cylinder. In a spark ignition engine, the mixture is then ignited using a spark from a spark plug. Ideally, the ignition of the fuel-air mixture should propagate from the spark through the mixture in an even, controlled manner. The resulting combustion drives the piston in the cylinder and generates torque for the engine.
To obtain optimum efficiency the spark is generally fired in advance of the top dead center (TDC) piston position. The degree of advance depends on the cylinder load and engine speed and can typically range from 60° before TDC to 10° after TDC. Generally engines running at higher engine speeds will operate with more spark advance, i.e. the spark occurs farther before TDC. Engines running at higher cylinder load will operate with less spark advance or a retarded spark.
In some cases, however, the combustion process does not proceed in an orderly fashion. For example, the fuel-air mixture may spontaneously combust outside of the flame envelope generated by the spark. In other words, high pressure and temperature in the cylinder, rather than the spark itself, may cause the air-fuel mixture to combust. This phenomenon is generally referred to as detonation. The use of low grade fuels tends to increase the likelihood of spontaneous combustion. Such spontaneous combustions are undesirable, since they generate a sharp increase in pressure within the working chamber. Repeated detonations can overheat and damage the engine.
In many conventional vehicle designs, there are systems for mitigating detonation. Some systems are designed to detect detonations and automatically retard the spark timing. That is, the sparking of the air-fuel mixture is performed later than before. This tends to weaken future combustions and reduce heat and pressure in the working chamber.
A problem with the above approach, however, is that it results in a drop in engine output. In response to the power loss, a driver may further depress the accelerator pedal. The depression of the accelerator pedal increases the cylinder load and may again drive up pressure and temperature levels in the working chambers and increase the likelihood of another detonation.